Phenolic compounds containing alkyl substituents in the ortho position on the ring are useful as starting materials for the preparation of polyphenylene oxide resins. In general, these compounds are prepared by catalyzed processes in which one or more phenolic compounds are reacted with an alkyl alcohol in the vapor phase. A number of specific procedures are described in the patent literature.
Processes designed for the ortho-methylation of phenols are disclosed by Hamilton, in U.S. Pat. Nos. 3,446,856 and 3,479,410. The first employs magnesium oxide as a catalyst at a temperature from 475.degree. to 600.degree. C. The second uses magnesium oxide or calcium phosphate, under similar conditions. In both cases, the magnesium oxide can be derived by thermal decomposition of magnesium carbonate, which can occur using the same temperatures as employed in the ortho-alkylation reaction. In addition, Van Sorge, in U.S. Pat. No. 3,972,828, describes an ortho-alkylation catalyst consisting of powdered magnesium oxide together with an inert polymeric binder.
Catalysts based on both magnesium and manganese have been found useful in ortho-alkylation reactions. Some of these are formed by co-precipitation, others by dry blending. In co-precipitation, manganous hydroxide is precipitated from a solution of a manganese salt in the presence of a magnesium source, e.g., magnesium carbonate. Precipitation can be induced by heating, by the addition of a caustic, e.g., potassium or sodium hydroxide, or addition of ammonium hydroxide. These kinds of procedures are described in copending U.S. applications Ser. Nos. 163,452 and 163,486, both filed Jun. 27, 1980 and assigned to the same assignee as herein. Dry blending techniques, on the other hand, are based in general on the admixing of magnesium oxides with manganese oxides or of compounds of the two which are capable of conversion into oxides upon calcination. See, for example, U.S. Pat. No. 3,873,628(mixing magnesium oxide and manganese sulfate, heating to dryness, and calcining), and U.S. Pat. Nos. 3,972,836 and 3,974,229(blending powders of magnesium oxide and manganese oxide).
Many of the above mentioned types of magnesium manganese catalysts suffer from shortcomings of one kind or another. Those which employ caustic co-precipitation techniques usually result in a catalyst which must be thoroughly washed to remove residual amounts of sodium or potassium ions. The use of ammonia is often objectionable because of the strong odor. Procedures in which sulfates are the manganese source can result in giving off malodorous fumes.